Stability of benzoporphyrin photosensitizers in water/ethanol mixtures: pKa determination and self‐aggregation processes

Benzoporphyrin monoacid derivatives, here named B3A and B3B, are promising new drugs for photodynamic therapy. Although both isomers show interesting characteristics as photosensitizing compounds, they have some distinct physicochemical properties such as the tendency to self‐aggregate in water‐rich media. Because pH drives the presence of each species, the pK_a of these compounds assumes strategic importance. However, traditional micro‐titration methods and UV–Vis absorption techniques fail to give reliable pK_a values due to the characteristics of this highly complex system, such as the precipitation of hydrophobic species, close pK_a values, and high absorption band superposition. In the present work, chemometric tools are employed to evaluate pK_a, and the kinetic tendency of monomers to undergo self‐aggregation is investigated. In solvent mixtures at low water percentage in ethanol, both B3A and B3B are stabilized in a monomeric state. However, in mixtures with a high water content, self‐aggregation takes place, mainly under a mild pH acid condition (3 < pH < 6), in which the prevalent protolytic species of both isomers is the neutral charged form, compounds with carboxylic and porphyrin free‐base groups. It is demonstrated that both isomers can undergo aggregation following a self‐catalytic mechanism, which is 2000 times slower to B3A than B3B. For B3A, the aggregation is manifested by a decrease in the monomer band with the aggregation band probably superposed to that of the monomer. For B3B, together with the decrease in the monomer band, a new band related to self‐aggregates is observed. Copyright © 2010 John Wiley & Sons, Ltd.     

Chaotic Expansion of Elements of the Universal Enveloping Algebra of a Lie Algebra Associated with a Quantum Stochastic Calculus

The functional Ito formula, in the form df() = f( + d ) –f(),is formulated and proved in the context of a Lie algebra L associatedwith a quantum (non-commutative) stochastic calculus. Here fis an element of the universal enveloping algebra U of L, andf() + d() – f() is given a meaning using the coproductstructure of U even though the individual terms of this expressionhave no meaning. The Ito formula is equivalent to a chaoticexpansion formula for f() which is found explicitly. 1991 MathematicsSubject Classification: primary 81S25; secondary 60H05; tertiary18B25.     

Immobilization of the [RuII(edta)NO+] Ion on the surface of functionalized silica gel

The reaction of NO and the immobilized dimer complex (edta)(2)Ru(2)(III(1/2),III(1/2)) on silica gel chemically modified with [3-(2-aminoethyl)aminopropyl]trimethoxysilane (AEATS) produces the corresponding immobilized nitrosyl complex AEATS/Ru(II)NO(+). This compound, a monomer, was obtained by reducing the immobilized ruthenium dimer either electrochemically or with Eu(II) and reacting this species with NO(2)(-) ions. The properties of [Ru(edta)NO](-) in solution and anchored (AEATS/Ru(II)NO(+)) on silica were compared using electrochemical (DPV, CV) and spectroscopic (IR, UV-vis, and ESR) techniques. The results indicate that immobilization does not alter the reactivity of the ruthenium complex and confirm that [Ru(edta)(H(2)O)](2)(-) may be used, either in solution or immobilized, as a catalyst for the conversion of NO(2)(-) to NO(+). Both the anchored nitrosyl complex AEATS/Ru(II)NO(+) and the [Ru(edta)NO](-) species in solution, upon one-electron reduction, liberate NO at comparable rates.     

Equilibria and spectroelectrochemical studies on the formation of multibridged tris(bipyrazine) ruthenium(II) complexes with ruthenium-edta groups

The tris(bipyrazine) ruthenium(II) complex forms a series of complexes containing [Ru(II/III)EDTA](2-/-) groups coordinated to the peripheral nitrogen atoms of the bipyrazine bridging ligand. These groups exhibit similar redox potentials (E(0) = 0.38 V vs. SHE) and a very weak electronic coupling through the central complex. When the peripheral Ru(III) groups are reduced to the Ru(II) state, strong charge-transfer bands appear at 490 and 670 nm and the stability constants increase by 7 orders of magnitude due to d(pi) -p(*)(pi) back-bonding interactions involving the peripheral ions and the bipyrazine ligand.     

Electronic and Resonance Raman Spectra of the μ-tris(Bipyrazine)ruthenium(II)-Hexaquis{ruthenium(II)EDTA} Supramolecular Complex

Abstract

Resonance Raman and electronic spectra of the μ-tris(bipyrazine)ruthenium(II)-hexaquis{ruthenium(II)EDTA} supramolecular complex are reported in this paper. Excitation in the 457–676 nm range leads to the selective enhancement of the Ru-bipyrazine vibrational peaks according to distinct patterns, supporting the assignment of the absorption bands at 670 and 490 nm as charge-transfer (MLCT) transitions from the [Ru^IIEDTA] d_π orbitals to the π₁? and π₂? LUMO levels of the bipyrazine ligand. A vibronic coupling mechanism involving the two excited states is suggested for the excitation at 490 nm. The occurrence of MLCT transitions in the [Ru(bpz)₃]²⁺ central unity, around 440 nm, is supported by the Raman and fluorescence excitation profiles.